We are requesting support for a Biological Imaging Core that will continue to perform an essential function for the projects associated with this PPG application. Based on the remarkable progress made by members of the PPG during the past grant period, it is clear that the research activities of all of the projects in this proposal are now poised at a point where morphological correlates are essential for placing biochemical and genetic information into a structural context. The Biological Imaging Core's prime purposes are as follow: First, the Core will provide technical support required for all aspects of preparation viewing and interpretation of thin section electron microscopy. A major aspect of EM use will be the availability of techniques for immunocytochemical localization of antigens using pre embedding immunogold labeling and post embedding localizations on frozen thin sections and sections of hydrophilic plastics. Second, the Core will support all aspects of light microscopic immunocytochemistry which is a critical technique for analysis of antigens expressed in cells. The Core will provide practical help with the use of the BioRad MRC 600 laser scanning confocal microscope and will continued to aid in the development of procedures for examination of tagged antigens and other fluorescent probes in live cells. All aspects of image analysis and reconstruction, quantitative analysis of digitized and data display and preparation for publication are available through the Core. Finally, an important aspect of the Core will to provide a focus for interaction amongst investigators in this PPG and to significantly aid in the planning, execution and interpretation of experiments through collaborations. Dr. Jamieson will serve as overall director of this ore; day to day operation of the Core will be carried out by Dr. Paul Webster who is conversant in all aspects of the preparation and analysis of material for light and EM immunocytochemistry. He will oversee the flow of work through the Core, assisted by Ms. Linda Chicione who provides general technical help with specimen preparation and darkroom work. Mr. Philippe Male will provide engineering support and training in the use of the confocal system and electron microscopes. All professionals associated with the Core are available for consultation on experimental approaches, technical advice and for collaborators on most of the projects in the PPG. Finally, a central responsibility of the staff will be training, supervision and quality control of new students and postdoctoral fellows who will participate in PPG projects.